diff --git a/mem0/memory/main.py b/mem0/memory/main.py
index 17b13bcba..ec14b6815 100644
--- a/mem0/memory/main.py
+++ b/mem0/memory/main.py
@@ -977,11 +977,11 @@ class Memory(MemoryBase):
                 }
                 
                 if operator in operator_map:
-                    result[key] = {operator_map[operator]: value}
+                    result.setdefault(key, {})[operator_map[operator]] = value
                 else:
                     raise ValueError(f"Unsupported metadata filter operator: {operator}")
             return result
-        
+
         for key, value in metadata_filters.items():
             if key == "AND":
                 # Logical AND: combine multiple conditions
@@ -2099,7 +2099,7 @@ class AsyncMemory(MemoryBase):
                 }
 
                 if operator in operator_map:
-                    result[key] = {operator_map[operator]: value}
+                    result.setdefault(key, {})[operator_map[operator]] = value
                 else:
                     raise ValueError(f"Unsupported metadata filter operator: {operator}")
             return result
diff --git a/tests/test_memory.py b/tests/test_memory.py
index 900d4db5d..6c8b69086 100644
--- a/tests/test_memory.py
+++ b/tests/test_memory.py
@@ -713,3 +713,47 @@ async def test_async_delete_memory_history_has_timestamps(mock_sqlite, mock_llm_
     assert call_kwargs["created_at"] == "2024-01-01T00:00:00+00:00"
     assert call_kwargs["updated_at"] is not None
     datetime.fromisoformat(call_kwargs["updated_at"])  # verify valid ISO timestamp
+
+
+@patch('mem0.utils.factory.EmbedderFactory.create')
+@patch('mem0.utils.factory.VectorStoreFactory.create')
+@patch('mem0.utils.factory.LlmFactory.create')
+@patch('mem0.memory.storage.SQLiteManager')
+class TestProcessMetadataFiltersMerge:
+    """Regression tests for issue #3952: multiple operators on the same key must be merged."""
+
+    def _make_memory(self, mock_sqlite, mock_llm_factory, mock_vector_factory, mock_embedder_factory):
+        mock_embedder_factory.return_value = MagicMock()
+        mock_vector_factory.return_value = MagicMock()
+        mock_llm_factory.return_value = MagicMock()
+        mock_sqlite.return_value = MagicMock()
+        from mem0.memory.main import Memory as MemoryClass
+        return MemoryClass(MemoryConfig())
+
+    def test_multiple_operators_same_key_merged(self, mock_sqlite, mock_llm_factory, mock_vector_factory, mock_embedder_factory):
+        """Filters like created_at: {gte: X, lte: Y} must preserve both operators."""
+        memory = self._make_memory(mock_sqlite, mock_llm_factory, mock_vector_factory, mock_embedder_factory)
+        result = memory._process_metadata_filters({
+            "created_at": {"gte": 1000, "lte": 2000}
+        })
+        assert result == {"created_at": {"gte": 1000, "lte": 2000}}
+
+    def test_single_operator_still_works(self, mock_sqlite, mock_llm_factory, mock_vector_factory, mock_embedder_factory):
+        """Single operator filters must continue to work."""
+        memory = self._make_memory(mock_sqlite, mock_llm_factory, mock_vector_factory, mock_embedder_factory)
+        result = memory._process_metadata_filters({
+            "created_at": {"gte": 1000}
+        })
+        assert result == {"created_at": {"gte": 1000}}
+
+    def test_multiple_keys_with_multiple_operators(self, mock_sqlite, mock_llm_factory, mock_vector_factory, mock_embedder_factory):
+        """Multiple keys each with multiple operators."""
+        memory = self._make_memory(mock_sqlite, mock_llm_factory, mock_vector_factory, mock_embedder_factory)
+        result = memory._process_metadata_filters({
+            "created_at": {"gte": 1000, "lte": 2000},
+            "score": {"gt": 0.5, "lt": 0.9},
+        })
+        assert result == {
+            "created_at": {"gte": 1000, "lte": 2000},
+            "score": {"gt": 0.5, "lt": 0.9},
+        }